Research On Wind Induced Aerodynamics Of Chamber Windbreak Along High-speed Railway

ABSTRACT:Installing windbreaks along the high speed railway is an effective measure to ensure high-speed train can still run safely under strong wind conditions.While ensuring the safety of the train,the windbreak must also have good wind-resisting ability and structure stability.The windbreak not only bears the aerodynamic load caused by cross wind,but also is affected by the wind induced aerodynamic impact caused by the high speed train passing through the windbreak area.Therefore,the wind-induced aerodynamic characteristics of windbreaks under cross wind and train induced wind should be mastered.At present,many achievements have been obtained in the study of high-speed railway windbreak at home and abroad,however,the research on its aerodynamic characteristics is still lacking.Especially for the chamber windbreak with new structure,its aerodynamic characteristics,dynamic characteristics of turbulent eddy,energy dissipation mechanism,fluid-solid coupling characteristics and fluid excitation effect need to be studied deeply.The chamber windbreak and CRH high-speed train are taken as research objects.The moving train model experiment,turbulent dynamics theory analysis and dynamic mesh numerical simulation methods are used.The aerodynamic characteristics of windbreak under the action of train wind and crosswind respectively and coupling,the fluid-solid coupling of the windbreak with train wind,the turbulent dynamic characteristics of the chamber windbreak's internal flow and outflow,the energy dissipation mechanism of the chamber windbreak and the influence of the chamber structure parameters on its aerodynamic characteristics and energy dissipation are studied.The fluid excitation characteristics of the windbreak-bridge model are investigated.The main research results include the following several parts:1.The"positive-negative-negative-positive"fluctuating law of wind pressure on the surface of windbreak is revealed.It is found that the pressure amplitude and pressure change rate are related to the square of velocity.With the increase of train speed,the pressure commutation time decreases.A comprehensive relationship between peak value of fluctuating pressure and train speed,installation distance and vertical height is established.At the same time,the phenomenon is found that there are more pressure reversing on the surface of windbreak when the train passing through the windbreak area by each other.And the extreme value of the pressure is greater than the situation when a single train passing through.2.The variation rule of aerodynamic load under the coupling of cross wind and train wind is revealed.The results show that the head train pressure impacts the cross-wind to resistance some of its energy;that the last train pressure coupled with the cross-wind,incresing the aerodynamic load of the windbreak.The negative pressure of the tail train makes the windbreak bear the maximum aerodynamic load with cross wind.When the angle of incoming wind is 90°,the aerodynamic load of windbreak reaches the maximum.The aerodynamic load value varies with the deviation angle.3.The quantitative description of the turbulent dynamic characteristics of the chamber windbreak's internal flow and outflow is given.It is found that the turbulent kinetic energy,reynolds stress and turbulence generation term in the chamber are much larger than those in the wake area.The new Omega criterion and classical Q and ?2 criteria are used to identify the coherent structure of vortex around the chamber windbreak.The results show that although the scale of the vortex inside the chamber is small,the energy is very high.It is the region where the vortex is generated and dissipated.The vortex scale in the wake region increases and the energy decreases.The fluid oscillation at the grooves of the leeward plate is the most intense.This reveals the energy dissipation mechanism of the large number of vortices induced by the porous structure of the chamber.The flow around the windbreak is divided into the upstream area,the chamber vortex area,the transition area and the wake vortex area.The ventilation rate has the greatest influence on the energy dissipation characteristics of the windbreak.The maximum energy dissipation coefficient appears in the range of 0.08 to 0.12 of the ventilation rate.4.The applicability of the numerical method based on virtual spring suspension model to simulate the flutter and vortex vibration of bridge is verified.This method is used to simulate the flutter characteristics and vortex vibration characteristics of the windbreak-bridge model.The conclusions are as follows:after installing windbreaks,the critical flutter speed of bridges is significantly reduced.The windbreak is not conducive to the anti flutter characteristics of the bridge.Meanwhile,the wind speed region and amplitude of bridge vortex vibration are significantly reduced.The windbreak is beneficial to the anti vortex vibration characteristics of the bridge.5.The moving train model test of fluctuating pressure on the surface of windbreak with a single train passing through and train passing by each other through windbreak area is completed for the first time.Four kinds of moving meshes which are train moving overset mesh,windbreak solid deformation mesh,fluid domain concomitant deformable mesh and far field floating boundary mesh are combined.Fluid-solid coupling of ultrathin porous plate windbreak has been realized for the first time.The research results can not only supplement the cognition of the pressure fluctuation law of windbreak surface,the wind induced fluid-solid interaction of windbreak,the turbulent dynamic characteristics of the flow around windbreak and the energy dissipation mechanism of chamber structure.It can also provide guidance and reference for the optimization design of high-speed railway chamber windbreak.